The long-term objective of this proposal is a better understanding of the genetics and biochemistry of mouse development. Through this, it seeks to provide the basis for a similar understanding of human genetics, development and disease. The work is focused on the genetic structure and biology of the t-region of mouse chromosome 17 and on the utilization of N-ethyl-N-nitrosourea (ENU) mutagenesis to obtain the mutants needed to genetically dissect that region. It investigates whether gene loci are rearranged in t-chromatin, as has been reported, and if chromosomal rearrangement is a sufficient explanation for the recombination inhibition exhibited by t-mutants. For these experiments, new mutations will be induced at specific loci in chromatin of the tw5-haplotype and their locations will be mapped. A second mutagenesis experiment includes participation in an endeavor whose goal is the isolation of all ENU-inducible lethals in the t-region, or at least a portion of it. Two experiments take a cellular and molecular approach to understand other unique properties of t-mutants. Development of an in vitro system for studying capacitation and fertilization by t/t sperm is proposed in order to learn more concerning the molecular basis for transmission ratio distortion in t males. The isolation of a family of embryonal carcinoma cell lines homozygous for the complete tw5-haplotype and several partial t-haplotypes derived from it is proposed to provide a cell culture system for t-mutant studies in general, and embryonic lethality studies in particular. In experiments unrelated to the t-region, ENU-mutagenesis will be used to produce mouse mutants which can serve as animal models of phenylketonuria and related hyperphenylalanemic conditions. The absence of such a model system seriously handicaps attempts to understand the fundamental pathology or to improve treatment of this genetic disease.